Migrate to Shoehorn
Why shoehorn?
shoehorn lets you pass partial data in tests while keeping TypeScript happy. It replaces as assertions with type-safe alternatives.
Test code only. Never use shoehorn in production code.
Problems with as in tests:
- Trained not to use it
- Must manually specify target type
- Double-as (
as unknown as Type) for intentionally wrong data
Install
bashnpm i @total-typescript/shoehorn
Migration patterns
Large objects with few needed properties
Before:
tstype Request = { body: { id: string }; headers: Record<string, string>; cookies: Record<string, string>; // ...20 more properties }; it("gets user by id", () => { // Only care about body.id but must fake entire Request getUser({ body: { id: "123" }, headers: {}, cookies: {}, // ...fake all 20 properties }); });
After:
tsimport { fromPartial } from "@total-typescript/shoehorn"; it("gets user by id", () => { getUser( fromPartial({ body: { id: "123" }, }), ); });
as Type → fromPartial()
Before:
tsgetUser({ body: { id: "123" } } as Request);
After:
tsimport { fromPartial } from "@total-typescript/shoehorn"; getUser(fromPartial({ body: { id: "123" } }));
as unknown as Type → fromAny()
Before:
tsgetUser({ body: { id: 123 } } as unknown as Request); // wrong type on purpose
After:
tsimport { fromAny } from "@total-typescript/shoehorn"; getUser(fromAny({ body: { id: 123 } }));
When to use each
| Function | Use case |
|---|---|
fromPartial() | Pass partial data that still type-checks |
fromAny() | Pass intentionally wrong data (keeps autocomplete) |
fromExact() | Force full object (swap with fromPartial later) |
Workflow
-
Gather requirements - ask user:
- What test files have
asassertions causing problems? - Are they dealing with large objects where only some properties matter?
- Do they need to pass intentionally wrong data for error testing?
- What test files have
-
Install and migrate:
- Install:
npm i @total-typescript/shoehorn - Find test files with
asassertions:grep -r " as [A-Z]" --include="*.test.ts" --include="*.spec.ts" - Replace
as TypewithfromPartial() - Replace
as unknown as TypewithfromAny() - Add imports from
@total-typescript/shoehorn - Run type check to verify
- Install:
